Method and apparatus for preserving rotor balance in cycloidal propellers



Oct. 1.1, 1960 E. ANDERSON 0 METHOD AND APPARATUS FOR PRESERVING ROTOR v BALANCE IN CYCLOIDAL PROPELLERS Filed Jan. '23,. 1958 2 Slants-Sheet 1 g s N 0 -D 'l O 0 m g a Q N IIlIlIII/I/II l/l/l/ll/l llllllll l 11/ 1/1/11 1 1/ I I //l l// ///I III i l Q O O a m EMIL E. ANDERSON I ATTORNEY Oct. 11, 1960 E. E. ANDERSON 2,955,660

METHOD AND APPARATUS FOR PRESERVING ROTOR v BALANCE IN CYCLOIDAL PROPELLERS' Filed Jan. 23, 1958 2 Sheets-Sheet 2 INVENTOR EMIL E. ANDERSON BY 3W ATTORNEY United States Patent METHOD AND APPARATUS FOR PRESERVING ROTOR BALANCE IN CYCLOIDAL PROPELLERS Emil B. Anderson, Seattle, Wash., assignor to Pacific Car and Foundry Company, Renton, Wash.

Filed Jan. 2'3, 1958, Ser. No. 710,812 1 Claim. or. 170-147 The rotors of cycloidal propellers are often internally stiffened by partitions formed so as to confine the blade mounting and control mechanisms. Voids remaining within the rotor are susceptible to flooding with consequent unbalancing of the rotor. My invention provides a method for filling these voids so as to displace any liquid which could subsequently flood it.

In propellers of the type improved by my invention, a drum-like carrier rotor is rotatably mounted in a ships hull with one end surface set flush with an unobstructed horizontal region on the underwater hull. This rotor, driven by the ships power plant, carries a plurality of flat, plate-like impeller blades, extending generally downward and rotatably mounted from equi-spaced positions near the periphery. As the ship is moved through the water, the rotary motion of the blades superposed upon the general unidirectional translation of the ships hull, and thus of the rotor as a whole, produces a generally cycloidal pattern of motion for each blade when viewed from fixed coordinates. In view of this motional pattern, propellers of this type are generally designated as cycloidal, and this designation should be understood to apply in the following description.

Cycloidal propellers provide a flexibility of control for a ships helmsman far surpassing that available with the more commonly used helical screw propeller combined with a rudder. In addition to controllable pitch of the driving blades, the full thrust available from the propeller may be directed horizontally at any desired angle with respect to the longitudinal axis of the ship. These important advantages are attended, however, by some problems which are peculiar to cycloidal propellers. For in order to produce an orbital motion of blades pivoted about axes generally parallel to the main axis of rotation, the supporting platform or hub must be of substantial lateral dimension. The blades, being attached at fill the void. The resulting unbalanced centrifugal force only one end, must be cantilevered in bearings which are separated by appreciable distance so as to counter the bending moment produced by blade loading while maintaining reasonable bearing loads. .Separation of the blade bearings imposes a requirement of minimum depth on the rotor drum, thereby fixing an appreciable vertical dimension of the blade carrying rotor. T hns compared to the axial hub of a helical screw propeller, the rotor of the cycloidal propeller is quite large.

Within this large volume bounded by the necessary external dimensions of the rotor drum, the propellerrnounting and blade-orientation control mechanisms occupy only a portion of the space. As these mechanisms must be immersed in lubricating oil, it is desirable to provide an internal compartment within the rotor housing of lateral dimension shaped to conform to the clearance required by the components to be enclosed. In this way it is not necessary to fill the whole drum with oil. Furthermore, the compartment walls, being formed as an integral part of the rotor, substantially increase the structural rigidity and load bearing ability of the rotor.

There is, however, one problem incident to the internal due to the confined mass of liquid produces severe reaction forces on the rotor bearings and ships hull which are quite undesirable.

My invention provides a solution to this problem which can be readily applied to new propeller rotors, as well as to old rotors already in service. I propose to preclude such unbalance by filling the void-volumes with a lowdensity unicellular material which is impervious to water and oils. The filler material is of a type which can be expanded and set from a liquid, so that only a small access hole is required to admit the liquid. Thus the propeller need not be disassembled to allow filling the voids.

It is thus an object of my invention to preclude flooding of the void compartments in a propeller rotor.

It is a further object of my invention to permit the enhanced rigidity and strength of a rotor attending internal compartmentation without danger of unbalance produced by accidental flooding of a compartment.

Yet another object of my invention is to fill the void space in a rotor with a material which is of very low density so as to add no appreciable weight to the rotor.

Still another object of my invention is to provide a filler material which is unaffected by contact with water and/ or oil.

Another object of my invention is to allow filling the voids in a propeller by injection of suitable material through a relatively small opening, thereby permitting my improvements to be applied to propellers which are already assembled.

These and other objects of my invention will become apparent from the following detailed description when taken together with the accompanying drawings, in which:

Fig. l is a sectional elevation through the vertical central axis of a cycloidal propeller showing the inside of a blade mechanism compartment on the right and a void compartment on the left which is filled with my fluid displacing cellular material; and

Fig, 2 is a cut-away view of the top of the rotor show ing the shape of the compartmenting partitions.

Referring now in detail to the drawings in which like reference characters denote like parts, the scheme of operation of propellers of the cycloidal type can be illustrated from Fig. 1. A detailed description of a similar propeller is given in a co -pending application Serial No. 710,771 so that only components essential to the rotation of the drum will be outlined here by way of illustration. A portion of the hull plating of a ship at the position where the propeller is to be located 1 is provided with a circular recess having cylindrical side walls 2 and top cover plate 3. Closely fitting the interior of this recess, a rotor, defined generally by cylindrical side walls 4 and top cover plate 5, is nested with bottom cover plates 6 and 7 set flush so as to continue the smooth contour of the outer hull 1. Rotatable support for the rotor is provided by its attachment to the flange shaped lower extremity of hub 8 which in turn is journaled in low-friction main-bearings 9 at the top and 10 at the bottom. Central cylindrical bosses 12 and 13 attached to the fixed structure provide seats for bearings 9 and 10. When the rotor is stationary, it is immersed in whatever buoyant liquid is supporting the ship. Liquid which fills the well bounded by walls 2 and 3 is prevented from leaking into the ships hull by seal 11 operative between the lower end of hub 8 and cylindrical central extension 13 of top cover plate 3.

In the usual application, power to drive the vertically disposed main rotor shaft 8 will come from a horizontally disposed output shaft 14 of the ships power plant. A right angle drive and speed reducer is provided by the use of a beveled pinion gear '15 attached to output shaft 14 and enmeshed with a larger beveled ring gear 16 which is centered on shaft 8 by supporting hub 17.

The primary purpose of the rotor housing is to provide a rotating mounting for the several propeller blades 18, one of which is indicated in Fig. 1. Optimization of propeller blade efliciency characteristics dictates use of a long, slender blade of high aspect ratio. Use of such blade configuration lowers the center of applied-thrust and thus imposes increased bending moment on the blade shank or cantilever supporting shaft 19. The resulting loads on lower bearing 21 and upper bearing 20 are kept within permissible limits by sufiicient depthwise dimension of the rotor housing which provides a mounting platform for the bearings. As a result, the rotor housing generally contains substantially more internal space than is necessary to satisfy the vertical space requirements of the blade orientation control system.

The considerable lateral extent of the regions outside the operating range of the blade support and control mechanisms can be appreciated from Fig. 2. Six times replicated void spaces, bounded top and bottom by drum plates and 6, respectively, are partitioned by radial wall members 22 and 24, and by circumferential members 23 at the inner well and 4 at the outside periphery of the drum. It is the volume inside these limits which is susceptible to filling in the event of failure or leaks in any of the walls and/or seams. Such leaks will not in general be of sufficient gravity to necessitate removal and repair of the rotor. Thus, if the impairment of operating characteristics can be avoided, such leaks need not be attended to until, because of some other reason such as regular servicing schedule or more severe damage, it becomes necessary to remove the rotor from the ship.

Thus I attain the objects of my invention by filling the void 3 defined by top and bottom walls 5 and 6, and vertical walls 4, 22, 23 and 24 with a suitable plastic material, generally designated in Figs. 1 and 2 by reference character 25. On viewing Fig. 2 it Will be seen that the plastic material 25 fills the voids 3 around the cylindrical side walls 4, thus filling the rotary drum adjacent the side walls where an unbalancing of the rotor would be more pronounced. There are a number of suitable filler materials 25 with which the voids in the cycloidal propeller rotor could be filled. One such material is commercially known as Stafoam LF 15254 manufactured by the American Latex Products Corporation. This material is a rigid, alkyd, thermosetting plastic, which can be foamed into place. To fill the void space in a cycloidal propeller, the plastic is prepared as a liquid and poured into the cavity through an opening generally designated as 5a having a plug 6a. A foaming reaction, similar to the temperature to 120 F. in a period of two hours. The

resulting density is between 3 to 5 pounds per cubic foot, which is only 5 to 8 percent the density of water or oil' which it is intended to displace. Once set, this material is resistant to water, oils and fuels which could possibly leak into the void compartment of a propeller.

While I have illustrated the reduction to practice of my invention with a particular design of cycloidal propeller, and a particular kind of filler material, it should be understood that other designs containing void spaces, as well as other filler materials could readily be employed byone skilled. in the art without departing from the spirit or letter of my invention as defined in the appended claim.

What I claim is:

In a cycloidal propeller, a drive shaft, a rotary drum attached to the drive shaft having substantially cylindrical side walls, an upper cover and a lower cover, a plurality of propeller blades projecting from the lower face of the rotary drum adjacent said side walls, said propeller blades being rotatably mounted thereon, a blade orientation control means centrally located in said drum, linkage connecting each blade to said orientation control means, partition walls diverging outwardly from the central orientation control means from the upper cover to the lower cover and surrounding said blade orientation control means and said linkage thereof, thereby defining a void space between adjacent propeller blade assemblies, the greater area of said void space being adjacent the inner periphery of the cylindrical side walls of the drum, and a filler of rigid alkyd thermosetting plastic of low density completely filling said void space so as to preclude flooding from the liquid in which the propeller is submerged and thereby preventing the unbalancing of the rotor.

References Cited in the file of this patent UNITED STATES PATENTS 2,224,326 Wahl Dec. 10, 1940 2,753,006 Franz July 3, 1956 FOREIGN PATENTS 485,102 Great Britain May 13, 1938 OTHER REFERENCES Plastics, volume XV, issue #155, April 1950, pages 93-95. 

